Powertrain
generic / SAE
P21B4
NOx Adsorber Over Temperature (Bank 1)
A temperature sensor at the NOx adsorber on bank 1 reports a value above the safe limit. Sustained over-temperature destroys the storage washcoat.
SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number1 / B4
Possible causes
- Runaway desulphation regeneration high
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Inspection / repair
- Difficulty: hard
- DIY: shop recommended
- Estimated cost: 200–4000 €
- Estimated time: 1.5–8 h
- Component: nox adsorber catalyst
- Component: exhaust temperature sensor
- MIL / check engine light
- emissions-relevant
- limp mode possible
Sources
References
sae:J2012